Synthesis of Silicone Magnetic Fluids for Use in Eye Surgery
Stable suspensions of superparamagnetic cobalt nanoparticles have been prepared in poly(dimethysiloxane) (PDMS) carrier fluids in the presence of poly[dimethylsiloxane-b-(3-cyanopropyl)methylsiloxane-b-dimethylsiloxane] (PDMS-PCPMS-PDMS) triblock copolymers as steric stabilizers. A series of the polysiloxane triblock copolymers with systematically varied molecular weights were prepared via anionic polymerization using LiOH as an initiator. These copolymers formed micelles in toluene or poly(dimethylsiloxane) (PDMS) carrier fluids and served as "nanoreactors" for thermal decomposition of the CO₂(CO)8 precursor. The nitrile groups on the PCPMS central blocks are thought to coordinate onto the particle surface, while the PDMS endblocks protrude into the reaction medium to provide steric stability. The particle size can be controlled by adjusting the cobalt to copolymer ratio. Ordered self-assemblies of these cobalt nanoparticles are observed when the dispersions are cast from toluene. Electron diffraction spectroscopy reveals that the cobalt nanoparticles have fcc crystal structures. TEM shows non-aggregated cobalt nanoparticles with narrow size distributions, which are evenly surrounded with copolymer sheaths. However, some degree of surface oxidation was observed over time, resulting in a decrease in magnetic susceptibility.
Novel poly[dimethylsiloxane-b-methyltriethoxysilylsiloxane-b-(3-cyanopropyl) methylsiloxane-b-methyltriethoxysilylsiloxane-b-dimethylsiloxane] (PDMS-PMTEOS-PCPMS-PMTEOS-PDMS) pentablock terpolymers were prepared. These terpolymers could fill the dual role both as steric stabilizers for preparing stable cobalt nanoparticle dispersions and precursors for the particle coating process. Silica films coated on the particles surfaces were employed to prevent the surface oxidation of the nanoparticles. Specific saturation magnetic measurement indicates that coating the nanoparticles with silica thin films can effectively inhibit the oxidation process.